Voltage Drop Horse Waterers Extended Run

[howardrichman]

recently; Ive posted a similar message of installing several horse waterers with the last load(s) 800+ ft away from a breaker source. I'm not sure what the accceptble E-drop should not exceed. (5%?) The total load may increase (taken middle of run) in the future, but for now is 1k+watts(250w each unit 500+watts per circuit). I'm not sure if these waterers should be derated any, depends on outside temps. I calculated 100% load @800+ ft 2 cks w/ shared nuetral, with a formula shows #8 or 6 copper esp for future waterers even figuring derating loads. I'de dout #10 could be used from the source, except when branched off the main line to a single load. Ive got to figure additional wateres could be added even @the longest run. Could anyone enlighten me on this?

Thanks;
HR...

 

[kwired]

Voltage drop with resistive load like this is not as critical as it is for a motor or some other loads.

If you have excessive voltage drop you are losing energy in the lines, but the load is simply using less energy, whereas a motor will draw even more current if the voltage is low and if too low for too long will overheat and fail.

Unless you are in an area where you experience freezing temperatures most of the year the lost energy in the lines may not be worth getting too carried away with making sure you have a really low voltage drop.

If you are in an area where there is not normally much freezing weather but the heaters are desired for just in case I would not be concerned with even 10 - 15% drop as you will not use these that much or that long that it is worth the extra copper vs the little wasted energy that will occasionally happen.

Running multiwire circuits does help.

 

[howardrichman]

Voltage drop with resistive load like this is not as critical as it is for a motor or some other loads.

If you have excessive voltage drop you are losing energy in the lines, but the load is simply using less energy, whereas a motor will draw even more current if the voltage is low and if too low for too long will overheat and fail.

Unless you are in an area where you experience freezing temperatures most of the year the lost energy in the lines may not be worth getting too carried away with making sure you have a really low voltage drop.

If you are in an area where there is not normally much freezing weather but the heaters are desired for just in case I would not be concerned with even 10 - 15% drop as you will not use these that much or that long that it is worth the extra copper vs the little wasted energy that will occasionally happen.

Running multiwire circuits does help.

Thanks for reply; In that case; a #8 or even 10GU would probally suffice, unless there are other future loads that would require less E-drop; unless the lines are for just waterers. I ran 1 1/2 pvc the 1st 550ft, then 1 1/4 to the remaining units to be safe for wire capacity and pulling ease; These horse farms seem to always add future loads in distant areas.

HR...

 

[ron]

Is there a chance they are going to ask you to install a convenience receptacle at the end of the run?

I agree if it is just the waterers, then you just need to be sure you have enough power (voltage and remaining current in the breaker/wire) left to keep the water from freezing, but if there is an outlet past the waterer, then you should keep the VD at or below 5% IMHO (although not a code requirement, just a good idea).

 

[weressl]

Voltage drop with resistive load like this is not as critical as it is for a motor or some other loads.

If you have excessive voltage drop you are losing energy in the lines, but the load is simply using less energy, whereas a motor will draw even more current if the voltage is low and if too low for too long will overheat and fail.

Unless you are in an area where you experience freezing temperatures most of the year the lost energy in the lines may not be worth getting too carried away with making sure you have a really low voltage drop.

If you are in an area where there is not normally much freezing weather but the heaters are desired for just in case I would not be concerned with even 10 - 15% drop as you will not use these that much or that long that it is worth the extra copper vs the little wasted energy that will occasionally happen.

Running multiwire circuits does help.

Some things to consider.

1. Resistive loads have a higher inrush than motors, unless they are 3 phase super-high-efficiency motors.
2. If the heaters are controlled by ambient sensing thermostats all heaters will be on at the same time, you can't utilize diversity factors.
3. If the actual water temperature is sensed the heaters will cycle and you have diversity, and your voltage drop wold improve.
4. Heater output drop will not be linear as P=(E^2)*R.

 

[kwired]

Some things to consider.

1. Resistive loads have a higher inrush than motors, unless they are 3 phase super-high-efficiency motors.
2. If the heaters are controlled by ambient sensing thermostats all heaters will be on at the same time, you can't utilize diversity factors.
3. If the actual water temperature is sensed the heaters will cycle and you have diversity, and your voltage drop wold improve.
4. Heater output drop will not be linear as P=(E^2)*R.

You have not been around livestock water tanks have you?

1. What difference does it make with this load if there is inrush current or not, as long as the overcurrent device allows starting. BTW I have never had to size a breaker up to 2.5 times the full load current to allow for starting on such a load but do so all the time for motors.

2-3. Each unit has individual control - they need to be able to heat as needed when temperatures are right around freezing, but also need to be able to heat practically continuously when it is -30F The more the animals are drinking the more heat there is coming from incoming water.

4. Heater output only becomes a problem in extreme cold conditions. Even then a unit without any significant drop can still get a layer of ice on top and around the edges but never freezes solid - which is usually the most important thing. In those conditions A water tank out in the open where conditions are even worse because of wind chill they typically do not have any animals using the tank as they have moved them to an area that at least has a wind break for the health of the animals. In that case they don't care if the thing gets a layer of ice (usually with a hole in it because of escaping heat) they mostly want enough heat inside to keep water pipe from freezing and bursting. It doesn't take very much heat to accomplish this, and the incoming water pipe is actually what keeps this from happening to some extent. It often is a 3/4 inch water pipe with about a 4 inch plastic pipe used as a sleeve down below frost line - heat from the ground rises through this sleeve and keeps the supply pipe from freezing, as long as all covers and insulation panels remain intact.

 

[gar]

121020-1101 EDT

A constant linear resistive load has a maximum possible peak current of Vp/R and for sine wave excitation this is Vrms/0.707 for Vp. This occurs twice each cycle. This is the kind of resistor that would be implied by the simple use of the word resistive.

An incandescent lamp may be loosely called a resistive load, and under certain constant steady state conditions the resistance is constant. But to say that a resistive load has a higher inrush current than a motor is not very clear unless the word resistive has some modifier added to it.

.

 

[howardrichman]

voltage drop

voltage drop

Is there a chance they are going to ask you to install a convenience receptacle at the end of the run? .

It all depends on where and load of the heaters; but the outlet or paddock lights could be somewhere on the line; so i could have a 10amp load somewhere on one or both phases on this line, or just run a parrell 3W line just for the additional loads.

HR...

I agree if it is just the waterers, then you just need to be sure you have enough power (voltage and remaining current in the breaker/wire) left to keep the water from freezing, but if there is an outlet past the waterer, then you should keep the VD at or below 5% IMHO (although not a code requirement, just a good idea).

..

 

[weressl]

121020-1101 EDT

A constant linear resistive load has a maximum possible peak current of Vp/R and for sine wave excitation this is Vrms/0.707 for Vp. This occurs twice each cycle. This is the kind of resistor that would be implied by the simple use of the word resistive.

An incandescent lamp may be loosely called a resistive load, and under certain constant steady state conditions the resistance is constant. But to say that a resistive load has a higher inrush current than a motor is not very clear unless the word resistive has some modifier added to it.

.

You're correct and I stand so. The inrush is dependent on the design, ie. how much the resistance will change from cold state to hot state. In the case if incandescent lights and hot plates for example, it is great and apprximately 12x, but heater that do not get glowing hot the resistance change is much smaller.

 

[weressl]

You have not been around livestock water tanks have you?

1. What difference does it make with this load if there is inrush current or not, as long as the overcurrent device allows starting. BTW I have never had to size a breaker up to 2.5 times the full load current to allow for starting on such a load but do so all the time for motors.

2-3. Each unit has individual control - they need to be able to heat as needed when temperatures are right around freezing, but also need to be able to heat practically continuously when it is -30F The more the animals are drinking the more heat there is coming from incoming water.

4. Heater output only becomes a problem in extreme cold conditions. Even then a unit without any significant drop can still get a layer of ice on top and around the edges but never freezes solid - which is usually the most important thing. In those conditions A water tank out in the open where conditions are even worse because of wind chill they typically do not have any animals using the tank as they have moved them to an area that at least has a wind break for the health of the animals. In that case they don't care if the thing gets a layer of ice (usually with a hole in it because of escaping heat) they mostly want enough heat inside to keep water pipe from freezing and bursting. It doesn't take very much heat to accomplish this, and the incoming water pipe is actually what keeps this from happening to some extent. It often is a 3/4 inch water pipe with about a 4 inch plastic pipe used as a sleeve down below frost line - heat from the ground rises through this sleeve and keeps the supply pipe from freezing, as long as all covers and insulation panels remain intact.

I have not recently had the need to drink from a horse-waterer.:lol:

When one considers something it will have either significant impact, negligible or none at all.

 

[kwired]

I have not recently had the need to drink from a horse-waterer.:lol:

When one considers something it will have either significant impact, negligible or none at all.

Well I can't speak for your experiences but based on your current location, these heaters are probably non existent, as any watering tanks that are in use there are probably not subjected to freezing.

Horses are different than cattle, they generally get to come indoors if the weather is brutal, but cattle are in such large herds it is impractical to do so most of the time. They will get moved to locations that have trees, buildings, or other items that will block wind but that is the most shelter they often get. They still need water. Many times a tank that is not in use has lids that can be closed and this helps contain heat. The units need individual thermostats or you can have large variance in water temperature based on many factors.

They generally use "non glowing" elements fastened directly to under side of drinking bowls, and cheap thermostats are just snap disc - thermostats also mounted to underside, the good thermostats are threaded bodies and the sensing surface is immersed directly into the water bowl, I honestly don't know what kind of mechanism is inside, probably is bimetal operated though, but of a better design (especially for the environment it is installed in) than a typical snap disc device.

 

[gar]

121022-0029 EDT

weressl:

A brand new 1000 W 120 V hot plate has a cold resistance (room temperature) of 15.7 ohms (Fluke 27).

By calculation from the nameplate rating the hot resistance is 120*120/1000 =14.4 ohms.

Measured just after plug-in 118 V and 8.09 A = 14.6 ohms, and at steady state very dull red 118 V and 7.84 A = 15.05 ohms (Kill-A-Watt EZ). This was about a 3% rise in resistance from cold to hot.

Contact resistance may be the reason the Fluke reading was somewhat higher.

.

 

[weressl]

121022-0029 EDT

weressl:

A brand new 1000 W 120 V hot plate has a cold resistance (room temperature) of 15.7 ohms (Fluke 27).

By calculation from the nameplate rating the hot resistance is 120*120/1000 =14.4 ohms.

Measured just after plug-in 118 V and 8.09 A = 14.6 ohms, and at steady state very dull red 118 V and 7.84 A = 15.05 ohms (Kill-A-Watt EZ). This was about a 3% rise in resistance from cold to hot.

Contact resistance may be the reason the Fluke reading was somewhat higher.

.

Hmmm, based on P/E=I it seems that you should be reading 8.47A @ 118V for a 1000W heater. Your reading results in 925.12W, almost 10% less than the nameplate claimed output.

 

[gar]

121022-1045 EDT

weressl:

I do not expect $15 hot plates to be precision resistors.

This mornings readings are:

Fluke 27 read 15.6 ohms. Subtracting 0.5 ohms lead resistance including minimal probe to probe contact resistance the hot plate becomes 15.1 ohms.

The Kill-A-Watt readings using V and watts were:

At start from room temperature 118.5 V, 960 W, calculates to 14.6 ohms. Calculate this resistance at 120 V and power is 986 W.

At steady state 118.2 V, 930 W, calculates to 15.02 ohms. Assume 120 V and this resistance dissipates 958 W.

In general when I measure small heaters the input power is less than the nameplate rated power. Incandescent bulbs I have measured are in general closer to their rating.

Comparison of Fluke 27 and Kill-A-Watt voltage readings:
Fluke 123.6, KAW 123.2 V.
Beckman 4410 123.41, KAW 123.0 V.

The KAW is reading about 0.4 V lower than Fluke or Beckman.

The KAW EZ is a fairly good and useful instrument at about $30.

.

 

[gar]

121025-0553 EDT

To further point out that a resistor does not have an inrush current different than its steady state instantaneous value at a comparable voltage phase angle see my photograph P5 at http://beta-a2.com/EE-photos.html .

In this particular instance I could never have gone to true steady state because the resistor would have burned out. Note this was 144 W into a 25 W resistor. Over a period of a number of cycles the current would have dropped due to an increase in the resistance from heating. But the implication of inrush is that something large occurs in the first cycle. The small little peak at the turn on point is an instrumentation anomaly.

By contrast see photo P1 for the characteristics of a tungsten filament incandescent bulb showing its potential large inrush current when turned on at a voltage peak. Also P2 for the much lower peak when turn on is at a voltage zero crossing.

.